Recently as ceramic material for high-speed cutting tools, a material having Al.sub.2 O.sub.3 as a major constituent or material which includes less than 1 percent by weight of a grain growth inhibitor replacing a corresponding percentage of the above Al.sub.2 O.sub.3 has been commonly used.
The present invention relates to a material produced by adding TiN to such Al.sub.2 O.sub.3 which has improved wear resistance and thermal shock resistance in high-speed cutting and a method for producing the material.
Based on the result of the study that TiN has low affinity with metal and has favorable heat conductivity, the inventors have found that a material to which TiN is added increases the wear resistance and thermal shock resistance when the material is used as a cutting tool.
However, when the material is produced by a conventional hot pressing sintering method, unfavorable phenomena such as the reaction between a carbon mold and TiN occur. Furthermore, such method requires an extremely high sintering temperature so that the grain size of the sintered body inevitably becomes excessively large. Still furthermore, the sintered body has different physical and mechanical properties between those on a plane perpendicular to the pressing direction and on a plane parallel to the pressing direction. Namely, anisotropy occurs among constituent grains so that such conventional method has hardly succeeded in obtaining material having favorable properties such as high strength, high wear resistance or high thermal shock resistance.
Accordingly, it is an object of the present invention to provide cutting tool material of improved strength, wear resistance and thermal shock resistance.
It is another object of the present invention to provide a cutting tool material which is most suitable for a high-speed continuous cutting operation.
It is a further object of the present invention to provide a method for producing such material by determining the optimal composition of raw material or powder mixture and the optimal producing conditions such as temperature or pressure.